The present invention relates to a method of estimating the overturn risk of a vehicle, in which the transverse acceleration of the vehicle is constantly determined, and as a function of the lateral acceleration, the rotational wheel speed behavior of the vehicle wheels is monitored.
From German Patent document DE 196 02 879 C1, a method of detecting the overturn risk of an ABS-equipped vehicle is known, during which the transverse acceleration of the vehicle is constantly monitored. When the transverse acceleration exceeds a defined limit value, a braking intervention takes place by means of a low testing brake power. In this case, it is monitored whether the testing brake power leads to an ABS intervention at the assigned wheel; that is, to a locking risk, which indicates that only a slight normal wheel force still exists or that the wheel has already lifted off the road and an overturn risk is present. Thus, solely the start of the ABS control intervention is used as an indication of an overturn risk.
It is an object of the invention to provide a method by means of which the overturn risk can be estimated still more reliably.
This object is achieved a method of estimating an overturn risk of a vehicle, in which the transverse acceleration of the vehicle is constantly determined, and as a function of the lateral acceleration, the rotational wheel speed behavior of the vehicle wheels is monitored. The overturn risk is determined redundantly, specifically a) as a function of whether the vehicle is braked or unbraked by monitoring the rotational wheel speed behavior, and b) by precalculating the rolling motion of the vehicle to be expected by using the transverse acceleration (atrans). Advantageous developments and further developments of the invention are contained in the subclaims.
The basic principle of the invention consists of a method by which the risk of a vehicle laterally overturning can be estimated redundantly, that is, by means of various submethods.
In the case of one submethod, the risk of overturn is estimated as a function of the actual braking state of the vehicle—braking or strong braking, or not braking or slight braking—by monitoring the rotational wheel speed behavior of the wheels on the inside of the turn.
In the case of another submethod, the rolling motion of the vehicle about its longitudinal axis is precalculated over a short time span of, for example, 0.5 s to 1.5 s on the basis of instantaneous movement parameters. The risk of overturn is assessed on the basis of the anticipated rolling motion.
The risk of a lateral overturn of the vehicle during cornering can, therefore, be better estimated by the sequential or parallel implementation of different monitoring methods.
For determining the risk of overturn, the transverse acceleration of the vehicle or the angular acceleration about the longitudinal axis of the vehicle is sensed in a continuous manner. The exceeding of a defined transverse acceleration limit value is a first indication that the vehicle is in a critical situation in which an overturn risk may exist.
The method of examining whether an overturn risk actually exists is carried out as follows:
a) As a function of whether the vehicle is braked or not braked, when a defined transverse acceleration is exceeded, the brake pressure is changed at individual wheels and the occurring rotational wheel speed behavior is monitored.
If the vehicle is not braked, individual or more wheels are simultaneously acted upon by a low test brake pressure. If, as a result of the test brake pressure, the rotational wheel speed does not change or changes only very little, this is an indication of a sufficiently high normal wheel force on the road; that is, the wheel is not in danger of lifting off the road. If, in contrast, the wheel is already braked intensively by the slight test brake pressure, this is an indication of a low normal wheel force or that the wheel has already lifted off the road.
If the vehicle is braked, the brake pressure at an individual or several wheels is simultaneously lowered and it is monitored whether the rotational wheel speed changes little or greatly. If the rotational wheel speed changes little or not at all, this is an indication that the wheel has already lifted off or is just about to lift off. If, in contrast, the wheel is relatively strongly accelerated, it can be concluded that a sufficient normal wheel force still exists.
b) In addition, by means of instantaneous movement parameters of the vehicle, the rolling motion is precalculated for a time span of, for example, 0.5 to 1.5 s. For this purpose, particularly the transverse vehicle acceleration, the time gradient of the transverse vehicle acceleration, as well as the frequency or the period of vibration of the rolling motion of the vehicle about its longitudinal axis can be used. By means of defined motion equations, into which diverse vehicle parameters are entered, such as the mass of the unloaded vehicle, the loading condition, the position of the center of gravity of the vehicle, etc., the rolling motion to be expected and, thus, the risk of overturn of the vehicle can be estimated. The time span for which an estimation can be carried out depends on the vehicle speed. The higher the vehicle speed, the earlier a critical situation has to be recognized.
When a critical driving condition, that is, the overturn risk of the vehicle is recognized, a control intervention of the braking system takes place, for example, selectively at individual wheels, whereby the overturn risk is reduced and the vehicle is stabilized. If a driving situation is estimated to be critical in a different fashion, the control interventions considered to be required for stabilizing the driving will therefore also differ. Preferably, the control intervention with the highest braking demand will then be selected. In addition, the ABS system of the trailer vehicle is permitted to reduce the selected braking demand, so that the vehicle motion can be controlled during cornering.
A particularly advantageous field of application of the invention is the commercial vehicle field because, specifically in this field, accidents occur repeatedly as a result of an overturn of towing vehicles or trailer vehicles during cornering or during abrupt steering movements in danger situations.
The method is particularly suitable for semitrailer units because dangerous driving conditions, which are caused by dynamic vehicle movements and would lead to the overturn of the semitrailer, can be recognized more reliably and a braking intervention can be carried out in time.
The method is preferably implemented in an electronic control unit (ECU), which may be arranged on the towing vehicle or the trailer vehicle or semitrailer. If the control unit is arranged on the towing vehicle, the control unit is connected by means of a connection line with the ABS system of the trailer.
In the following, the invention will be explained in detail by means of an embodiment in connection with the drawing.